Hybrid matching network topology

ABSTRACT

The present disclosure relates to plasma generation systems which utilize plasma for semiconductor processing. The plasma generation system disclosed herein employs a hybrid matching network. The plasma generation system includes a RF generator and a matching network. The matching network includes a first-stage to perform low-Q impedance transformations during high-speed variations in impedance. The matching network includes a second-stage to perform impedance matching for high-Q impedance transformations. The matching network further includes a sensor coupled to the first-stage and the second-stage to calculate the signals that are used to engage the first and second-stages. The matching network includes a first-stage network that is agile enough to tune each state in a modulated RF waveform and a second-stage network to tune a single state in a RF modulated waveform. The plasma generation system also includes a plasma chamber coupled to the matching network.

BACKGROUND

In semiconductor manufacturing, plasma processing chambers utilize radiofrequency (“RF”) power to generate plasma. Plasma is typically createdand maintained by an electric current alternating at an RF frequency,which excites and ionizes the source gas used in the plasma chamber.Plasma processing chambers may be used for industrial processes such as,but not limited to, surface treatment of materials or plasma etchingduring a semiconductor fabrication process. To achieve efficient powertransfer between a RF generator and a plasma load, an impedance-matchingnetwork is generally used to match a load impedance to a sourceimpedance (e.g., 50 Ohms).

The plasma chamber presents electrical impedance that may vary greatlyand quickly. It is important that the output impedance of the RF powergenerator be closely matched to the rapidly-changing load impedance ofthe plasma chamber to avoid damaging reflections of power back into theoutput circuitry of the RF power generator, which can occur when theimpedances are mismatched. Impedance matching devices (e.g., matchingnetworks) are used to match the load impedance of the plasma processingchamber to the output impedance of the RF power generator. Forrapidly-varying load impedance, the matching network has to dynamicallymatch the impedance accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, examples inaccordance with the various features described herein may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawings, where likereference numerals designate like structural elements.

FIG. 1 is a block diagram of a hybrid matching network, according to asystem and method of the present disclosure.

FIG. 2 is an illustration of a hybrid matching network topology,according to a system and method of the present disclosure.

FIG. 3 is a Smith Chart which displays a tunable range for a hybridmatching network with a first-stage matching network with eight switchterminals. The tunable range illustrated in this Smith Chart correspondsto the hybrid matching network topology of FIG. 2.

FIG. 4 is a Smith Chart which displays a tunable range for a hybridmatching network with a first-stage matching network with six switchterminals.

FIG. 5 is a Smith Chart which displays a tunable range for a hybridmatching network with a first-stage matching network with ten switchterminals.

FIG. 6 is a Smith Chart illustrating an impedance transformation to tunea load impedance to a source impedance, according to a system and methodof the present disclosure.

FIG. 7 is a Smith Chart illustrating an impedance transformation tomatch a load impedance to a target impedance, according to a system andmethod of the present disclosure.

FIG. 8 is a flowchart of a method to perform impedance matching,according to a system and method of the present disclosure.

DETAILED DESCRIPTION

The description of the different advantageous implementations has beenpresented for purposes of illustration and is not intended to beexhaustive or limited to the implementations in the form disclosed. Manymodifications and variations will be apparent to a person havingordinary skill in the art. Further, implementations may providedifferent advantages as compared to other implementations. Theimplementation or implementations selected are chosen and described tobest explain the principles of the implementations, the practicalapplication, and to enable a person having ordinary skill in the art tounderstand the disclosure for various implementations with variousmodifications as are suited to the particular use contemplated.

Before the present disclosure is described in detail, it is to beunderstood that, unless otherwise indicated, this disclosure is notlimited to specific procedures or articles, whether described or not. Itis further to be understood that the terminology used herein is for thepurpose of describing particular implementations only and is notintended to limit the scope of the present disclosure.

During plasma processing, a radio frequency (“RF”) generator transmitsRF alternating current (“AC”) waves through RF transmission lines andnetworks to a plasma processing chamber. To provide an efficienttransfer of power from the RF generator to the plasma processingchamber, a matching network is employed to transform the time-varyingimpedance presented by the plasma chamber to the optimal load impedanceof the RF generator.

Many RF matching networks have variable capacitors and a control circuitwith a microprocessor to control the capacitance values of the variablecapacitors. There may be various configurations of RF matching networks.Herein, a vacuum variable capacitor may be defined as anelectro-mechanical device which has two concentric metallic rings thatare moved in relation to each other to change capacitance. The value andsize of the variable capacitors within the RF matching network may bedetermined by the power handling capability, frequency of operation, andimpedance range of the plasma processing chamber.

Pulse-Frequency Modulation is a commonly used technique to deliver powerin plasma processing systems. Herein, Pulse-Frequency Modulation Is amodulation method where the amplitude of the carrier waveform is variedbetween at least two discrete power levels at some frequency with someduty cycle. As such, power delivered in a pulse-waveform may affectplasma characteristics which may therefore cause the electricalimpedance of the plasma chamber to vary with each pulse waveform. At theonset of each pulse, a spike in reflected power can result.

Many RF plasma generation systems employ multi-level pulsing for variousdifferent power states. Each power state may be associated with a uniqueimpedance because the characteristics of the plasma may change based onthe delivered power to the plasma chamber. During plasma processing, theplasma changes occur very quickly (e.g., at a rate of up to hundreds ofthousands of Hertz). Many matching networks, such as those that havevacuum variable capacitors, generally react on the order of hundreds orthousands of milliseconds.

Accordingly, many of these matching networks are limited to latching onto one of the multi-level power states (e.g., high or low amplitudes).For example, for dual level pulsing, a matching network may latch on tothe high amplitude or to the lower amplitude state and maintain positionfor the duration of the other state. This means that the system willbehave optimally during one state, and sub-optimally for any otherstates.

The present disclosure provides a mechanism to match to all states byreacting to all impedance states to maintain a low-reflectioncoefficient during impedance variations. Advantageously, the presentdisclosure reduces the tuning time in matching networks. Herein, tuningtime is defined as the amount of time that it takes for a matchingnetwork system to reach a tuned state from a detuned state.

FIG. 1 is a block diagram of a hybrid matching network 100, according toa system and method of the present disclosure. Advantageously, thehybrid matching network 100 disclosed herein employs a two-stage tunablematching network. As shown, the hybrid matching network 100 receives itsRF input from a RF generator at RF input 109, the first-stage matchingnetwork 101 (e.g., a switch network), the second-stage matching network103 (e.g., a mechanically-tuned matching network), a sensor element 102,and plasma chamber 104 (e.g., load) which are all coupled to one or moretransmission lines 105-108. Herein, a hybrid matching network 100 may bedefined as a multi-stage matching network which can operatesimultaneously or in sequence to tune a load impedance to a target(e.g., source) impedance.

The first-stage matching network 101 may be responsible for matching tohigh-speed variations in impedance during different stages of a RFwaveform and a second-stage matching network 103 may be responsible forhigh-Q impedance transformations. Accordingly, in severalimplementations of the present disclosure, the bulk of the impedancetuning is performed by the second-stage matching network 103, for high-Qtransformations and the first-stage matching network 101 can be used totune system impedance for low-Q transformations that arise from a pulsedwaveform, changes in chamber conditions, or other factors. Herein,high-speed variation is defined as a change in impedance that is beyondthe control loop bandwidth associated with a second-stage matchingnetwork.

The first-stage matching network may include fixed capacitors and PINdiodes, silicon-carbide field effect transistors (SiCFETs), metal oxidefield effect transistors (MOSFETs), insulated gate bipolar transistors(IGBTs), or bipolar junction transistors (BJTs) electronic switches andthe second-stage matching network may include vacuum variablecapacitors, or air variable capacitors, and stepper motors, brusheddirect current (DC) motors, brushless DC motors, or AC motors.

Advantageously, the hybrid matching system as disclosed herein canreduce the stress on the high-speed, secondary matching network (e.g.,the first-stage matching network 103) and can assist in dialing in thematching network to tune the plasma system to a target impedance.

Herein, high Q or low Q refers to a high or low-quality factor. TheQ-factor is defined as the ratio of energy stored in a system to theamount of energy dissipated in a system. Q-factor is a dimensionlessunit and, for a single element, is expressed as the ratio between theelements reactance and its resistance. In a matching network, theminimum Q-factor is the configuration where the least amount of energyis stored for the transformation to be accomplished.

In some implementations, a high-Q impedance transformation is one thathas a Q-factor that is greater than two whereas a low-Q impedancetransformation is one that has a Q-factor that is less than two.

FIG. 2 is an illustration of a hybrid matching network 200 topology,according to a system and method of the present disclosure. The hybridmatching network 200 topology illustrates a first-stage matching network201, a second-stage matching network 202, and a sensor element 203coupled thereto. In some implementations, the bulk of the tuning isperformed by the second-stage matching network 202 whereas thefirst-stage matching network 201 can be employed to implement “coarsetuning” for low-level and fast impedance variations.

The voltage and current sensed at an output (e.g., node 209/215) of thefirst-stage matching network 201 can be used to direct both stagessimultaneously as they act independently. The RF power is delivered by aRF generator to the system input node 208, which is delivered to aplasma chamber (not shown) by way of the hybrid matching network 200.

In the implementation shown, the first-stage matching network 201includes an impedance transformer 217 with banks 205, 206 of switchterminals 210 (e.g., switched capacitors) on two sides of the impedancetransformer 217. Collectively, the impedance transformer 217 and thebanks 205, 206 of switch terminals 210 (e.g., switched capacitors)provide the first-stage matching network 201 the flexibility to matchimpedances, within a specified range. The impedance transformer 217 mayinclude a lumped-element pi network or a distributed network such as atransmission line to achieve the desired impedance transformation. Forexample, the impedance transformer 217 may include a pi network sectionto perform both a step-up and step-down impedance transformation to tuneto a target impedance.

The specified range of the first stage is a design choice which can bemade based on the application and the availability of devices at a givenfrequency and power level. Choosing a narrow range may limit stress onthe first stage for a given frequency and power level, but also limitsthe applications in which it may be used. Choosing a large range has theopposite consequence. In either case, the system may function similarly.

Accordingly, the present disclosure provides an impedance transformer217 to be used in conjunction with banks 205, 206 of switch terminals210 (e.g., switched capacitors) to tune an impedance. The impedancetransformer 217 may be realized by inserting a section of a transmissionline with appropriate electrical length and characteristic impedance.For example, a quarter-wave impedance transformer may be used to matchreal impedances. However, a complex load impedance can also betransformed to a real impedance by adding a series or shunt reactivecomponent. Notably, a quarter-wave transformer can provide a match at aparticular operating frequency as well as an acceptable match across abandwidth of one octave, or less, depending on the quality factor, Q, ofthe transformation and the application.

In the implementation shown in FIG. 2, the impedance transformer 217includes a lumped-element pi network. The impedance transformer 217performs the same impedance transformation as the transmission line orwaveguide and can be made much more compact at lower frequencies butoffers a more limited bandwidth. In one implementation, the impedancetransformer 217 of lumped elements consists of capacitors 213, 214 inshunt network branches in addition to an inductor 216 in a seriesbranch.

The banks 205, 206 of switches 212 each include individual (e.g., RF)switch terminal 210 (in each respective banks 205, 206 of switches 212)which include switches 212 and reactive tuning elements 221 which allowthe first stage to match a variety of load impedances. In someimplementations, a look-up table stored in a memory element (not shown)of the hybrid matching network 200 may be referenced to determine thestate of the switches 212 to collectively tune the output impedance ofthe first stage to a complex conjugate of the calculated input impedanceof the second-stage matching network. In the implementation shown inFIG. 2, the banks 205, 206 each include four switch terminals 210 ofswitches 212 and therefore eight switch terminals 210 to effectimpedance tuning. As will be described in more detail with respect toFIGS. 3 and 4, the number of switch terminals 210 can affect the tuningprecision of the first-stage matching network 201.

In addition, a switch actuator 204 is coupled to each switch terminal210 for each bank 205, 206 of switch terminals 210. Herein, a switchactuator is defined as the portion of the system responsible forbringing a switch terminal 210 into, or out of, the circuit by engaging(e.g. close) or disengaging (e.g. open) the switch 212 in that switchterminal 210. The switch actuator 204 may be coupled to the banks 205,206 of switch terminals 210 by electrical, magnetic, optical, ormechanical means. In the implementation shown, the switch actuator 204is coupled to the eight switches 212 in the banks 205, 206 of switchterminals 210. In addition, the switch actuator 204 is coupled to thesensor element 203. The sensor element 203 may operate the switchactuator 204 to engage the first-stage matching network 201.

The state of the switches 212 of the banks 205, 206 of switch terminals210 may be expressed in a binary format. For example, a first-stagematching network 201 with the switches 212 of bank 205 all being closedand the switches 212 of bank 206 being open may be expressed as [11110000]. Likewise, a first-stage matching network 201 with the first halfof the switches 212 of banks 205, 206 being open and the second half ofthe switches 212 of banks 205, 206 being closed may be expressed as[0011 0011]. In one implementation, a look-up table may be used torelate the proper configuration states of the switch terminals 210 tothe readings from sensor element 203. In this case, after sensor datahas been received and processed, the switch terminals 210 can beactuated to a set of states that minimizes the reflection coefficient(e.g. gamma) at the input 208 of the first stage.

The sensor element 203, as shown, is coupled to an input 215 of thesecond-stage matching network 202. The sensor element 203 can detectvoltage and current, or forward and reflected coupled waves. The sensorelement 203 may be a voltage and current sensor, or a bi-directionalcoupler which detects the voltage, current, forward, or reflectedwaveforms. In particular, the sensor element 203 measures voltage andcurrent and calculates the relationship between the measured voltage andcurrent in both phase and magnitude. Moreover, the sensor element 203can detect high-speed variations in plasma chamber impedance and can usethe change in impedance caused by the high-speed variations to engagethe first-stage matching network 201.

It should be understood by a person having ordinary skill in the arthaving the benefit of this disclosure that the magnitude ratio and phaserelationship of voltage and current waveforms at a particular node in amatching network can be used to direct the tunable elements in anautomatic matching network. In this case, a notable aspect is thelocation of the sensor, and the types of information it gathers. Themagnitude ratio and phase relationship of these quantities at the nodewhere sensor element 203 exists in the system allow us to drive thesecond-stage matching network matching network as well as actuate theswitch terminals 210 in the first-stage matching network simultaneously.In this implementation, magnitude and phase are used to drive thetunable elements in the second-stage matching network matching network,and those same values are used to calculate the input impedance to thesecond-stage matching network, which is the load impedance for thefirst-stage matching network. When this impedance is computed, theswitch terminals 210 are actuated such that the output impedance of thefirst stage is the complex conjugate of the calculated load impedance.These operations occur simultaneously and independently. As thesecond-stage matching network self-adjusts its tunable elements toachieve a minimization of gamma looking into its input 215, it isconstantly presenting some load at the input to the first stage.Therefore, under any circumstance where the impedance looking into node215 is approximately the complex conjugate of one of the availableconfigurations of switch terminals 210, the first stage can minimizegamma looking into node 208, which is the input to the hybrid matchingsystem. As the second-stage matching network continuously drives towardsminimum gamma at node 215, the first stage can continue to actuateswitch terminals 210 to maintain the most optimal impedance match atnode 208.

FIG. 2 also shows an illustration of the second-stage matching network202. In some implementations, the second-stage matching network 202 maybe configured similarly to conventional matching networks. For instance,the second-stage matching network 202 may include one or more variablecapacitors 218, 219 and an inductor 220. The variable capacitors 218,219 may be adjusted, for example, by a lead screw (not shown) in amechanical means (e.g., using motors 211) to transform the impedancepresented by a plasma chamber (not shown) to match a target impedance(e.g., source impedance, typically 50 ohms).

FIG. 3 is a Smith Chart 300 which displays the tunable range 302 for thefirst stage of a hybrid matching network system that contains eightswitch terminals 210 (see FIG. 2). The tunable range illustrated in thisSmith Chart corresponds to the first-stage matching network of thehybrid matching network topology of FIG. 2. Notably, the Smith Chart 300reflects the hybrid matching network 200 topology illustrated in FIG. 2in which the first-stage matching network 201 has eight switch terminals210. The tunable range 302 illustrated in FIG. 3 is the conjugate of therange of (e.g., load) impedances of which a first-stage matching networkcan transform to the target impedance (e.g. 50 ohms in this example).

In some implementations, the profile (e.g. shape) of the tunable range301 can differ from this example. The profile of the tunable range 302may be determined by the topology of the first-stage matching networkand the value of the reactive tuning elements. In this example, thevalues of reactive tuning elements 221 in switch terminals 210, and thevalue of the reactive elements 213, 214, 216 in the impedancetransformer 217 shown in FIG. 2 may determine the profile of the tunablerange 302.

Most notably, because the first-stage matching network is a discretesystem with a finite number of configurations, the number of switchterminals 210 (see FIG. 2) within the first-stage matching network of ahybrid matching network determines the density of the tunable range 302.Accordingly, the greater the number of switch terminals within thefirst-stage matching network, the greater the density of the resultingtunable range 302. In some implementations, eight switch terminals maybe sufficient for applications that can tolerate a small amount of gammaat the input of the hybrid match system. As such, the number of switchterminals designed for a first-stage matching network may account for atarget VSWR.

The tunable range 302 includes an impedance grid 306 of orthogonal arcs307, 308. Each successive arc represents one increment in the totalvalue of reactance in switch banks 205 and 206 (see FIG. 2)respectively. Load impedances that are the conjugate value of one of theintersections of 307 and 308 can be transformed to the target impedanceprecisely. Load impedances that fall in between these intersections,such as impedance point 305, can be very nearly transformed to thetarget impedance by choosing the switch configuration that most nearlyrepresents the conjugate of that load impedance.

For example, an impedance point 303 within the tunable range 302 liesdirectly at the intersection of horizontal and vertical impedance arcs307, 308. Accordingly, the first-stage matching network can tune thisload impedance to match a source impedance with a high-degree ofprecision (e.g., 50+0.3j Ohms for a 50-Ohm source impedance). Incontrast, the first-stage matching network can tune a load impedancepoint 305 to a source impedance with moderate-to-high precision (e.g.,50.5−2.4j Ohms).

In addition, the first-stage matching network of the hybrid matchingnetwork can tune a load impedance that is outside of a VSWR 301 butwithin the tunable range 302. For example, the load impedancerepresented by impedance point 304, which notably lies directly at theintersection of horizontal and vertical impedance arcs 307, 308, can betuned directly to the source impedance with high-precision. Accordingly,the load impedance that is directly on arcs 307, 308 of the impedancegrid 306 may be tuned directly to a source impedance regardless of thedistance the load impedance is from the source impedance.

As previously discussed, the profile of the tunable range 302 may bedetermined by the total value of the reactive tuning elements 221 (seeFIG. 2) in the switch terminals 210 and an impedance transformer. It maybe advantageous to have the range of the first stage matching networkskewed in one direction or another for specific applications where thedirection of impedance shifts due to pulsing or other operationalparameters of a plasma chamber or individual process are known and wellcharacterized.

FIG. 4 and FIG. 5 show the tunable range for two possibleimplementations of the first stage matching network. The differencebetween these two implementations is the number of switch terminals. InFIG. 4 the number of switch terminals is six, or three per bank, whichyields tunable range 401. In FIG. 5 the number of switch terminals 210is ten, or five per bank, which yields tunable range 501 on the SmithChart 500. The gaps between discrete switch configurations are larger inFIG. 4 than FIG. 5; therefore, the worst-case impedance match can beless acute in a system with six switch terminals than a system with tenswitch terminals.

FIG. 6 is a Smith Chart 600 illustrating an impedance transformation totune a load impedance of 53−j30 ohms (impedance point 601) to a targetimpedance (in this case, 50 ohms), according to a system and method ofthe present disclosure. In the example shown, a first-stage matchingnetwork of a hybrid matching network was employed to tune a loadimpedance to within a target VSWR 606 (e.g., to impedance point 602).

FIG. 6 further illustrates impedance curves 603-605 which represent thetransformation of voltage and current in phase and magnitude through thefirst-stage matching component of the hybrid matching network. In theexample shown, the impedance curve 603 is associated with a first bankof switches (e.g., on a first end of the impedance transformer) whereasthe impedance curve 605 is associated with a second bank of switches(e.g., on a second end of the impedance transformer). Furthermore, theimpedance curve 604 is associated with an inductor element of theimpedance transformer. Collectively, curves 603-605 show a pathway inimpedance transformation that the first-stage matching network undergoesto tune a load impedance to a target (e.g., source) impedance (e.g.,impedance point 602) in a single step. As previously discussed, thefirst-stage matching network can tune a load impedance to a targetimpedance with high precision in various implementations. For example,impedance point 602 is close to 50 Ohms (e.g., 48.4−2.8j Ohms) for atarget impedance of 50 Ohms.

FIG. 7 is a Smith Chart 700 illustrating an impedance transformation tomatch a load impedance 701 to a target impedance 709, according to asystem and method of the present disclosure. This example is given tofurther demonstrate the advantages gained by using a hybrid matchingnetwork with the sensor arrangement as it is disclosed. Because thetuning goals of either stage network may be completely independent, bothcontrol loops may operate simultaneously without any unwantedinteractions. In the example shown, a hybrid matching network wasemployed to tune a load impedance 701 of 1−j31 ohms to a targetimpedance 709 of 50 ohms. FIG. 7 depicts a Smith Chart 700 and impedancecurves 702-707 which represent the path taken to transform the loadimpedance 701 to the target impedance 709 through the first andsecond-stage matching networks of the hybrid matching network.

In the example shown, the impedance curves 702-704 are associated withthe impedance transformation attributed to the device elements of thesecond-stage matching network of a hybrid matching network. Similarly,the impedance curves 705-707 are associated with the impedancetransformation attributed to the device elements of the first-stagematching network of a hybrid matching network. For example, theimpedance curves 705-707 are associated with the impedancetransformation attributed to capacitors within a first bank of switchterminals (i.e., curve 707), an inductor device element of the impedancetransformer (i.e., curve 705), and the capacitors within a second bankof switch terminals (i.e., curve 706) of the first-stage matchingnetwork of the hybrid matching network. This example uses the topologieschosen in FIG. 2, where the first-stage matching network 201 (see FIG.2) is a pi network with two banks 205, 206 of switch terminals 210 andthe second-stage matching network 202 (see FIG. 2) is a step-down Lnetwork which includes a variable shunt capacitor, a variable seriescapacitor, and a fixed series inductor. It should be obvious to a personhaving ordinary skill in the art having the benefit of this disclosurethat this hybrid matching system could employ alternative networktopologies for the first-stage matching network and the second-stagematching network, so long as doing so does not depart from the spiritand scope of the present disclosure.

In the example, the load impedance 701 of 1−31j is transformed by thesecond-stage matching network to 28.4+8.2j. When the sensor 203 (seeFIG. 2) calculates an impedance within the tunable range of thefirst-stage matching network, the first-stage matching network maybecome active. The switches 212 (see FIG. 2) may be actuated to theconfiguration that most nearly matches the conjugate of the calculatedload impedance. From the moment that the switches 212 (see FIG. 2) arecorrectly actuated, the reflection coefficient at the input of thesystem may be minimized. The second-stage matching network may continueto drive to minimize the reflection coefficient at its input 215 (seeFIG. 2). As the impedance looking into node 215 (see FIG. 2) changes bythe motion of the tunable elements and the load presented by the plasmachamber, the first-stage matching network may still be active, providedthe impedance looking into node 215 (see FIG. 2) is still within itstunable range. Even as those operations continue, from the overallsystem perspective, the tuning goal has already been achieved.

Still referring to FIG. 7, the impedance curve 707 is associated with afirst bank of switches (e.g., on a first end of the impedancetransformer) whereas the impedance curve 706 is associated with a secondbank of switches (e.g., on a second end of the impedance transformer).Furthermore, the impedance curve 705 is associated with an inductorelement of the impedance transformer. Collectively, curves 705-707 showa pathway in impedance transformation that the first-stage matchingnetwork undergoes to tune a load impedance to a target (e.g., source)impedance (e.g., impedance point 709). As previously discussed, thefirst-stage matching network can tune a load impedance to a targetimpedance with high precision in various implementations. For example,impedance point 709 is close to 50 Ohms (e.g., 50.2−0.4j Ohms) for atarget impedance of 50 Ohms.

FIG. 8 is a flowchart 800 of a method to perform impedance matchingaccording to a system and method of the present disclosure. Flowchart800 begins with detecting a RF signal (block 801). The RF signal may bedetected by a sensor element, a component of the hybrid matchingnetwork. If the detected RF signal is greater in amplitude than apre-determined threshold which is defined according to an application,the sensor performs calculations (e.g., phase error, magnitude error,and impedance) necessary to begin the tuning procedure (block 805). Ifthe amplitude of the phase and magnitude error is not higher than thepre-determined threshold, and the calculated impedance is not inside thetunable range of the first-stage matching network, then both stagesmaintain their pre-set positions (block 802, 804). These pre-setpositions are application dependent and can exist anywhere within theusable range of the tunable elements in the network.

In addition, if the error signals generated by comparing the magnitudesand phase relationship of voltage and current are above some threshold,then they can be used to tune the variable elements in the second-stagematching network (block 808). If the input impedance at node 215 (seeFIG. 2), calculated from the difference in magnitude and phaserelationship of voltage and current, is within the tunable range of thefirst-stage (block 807) then the switch terminals can be actuated to theconfiguration that causes the output impedance of the first-stage tomatch the complex conjugate of the calculated load impedance (block809). If the phase and magnitude derived error signals are smaller thansome threshold, while RF is detected at a sufficient level, the tunableelements in the second-stage matching network can remain at theircurrent position as the tuning goal has been achieved (block 802). Thefirst-stage matching network can continuously monitor the calculatedinput impedance to node and change its configuration to minimize thereflection coefficient seen at its input.

Although the present disclosure has been described in detail, it shouldbe understood by a person having ordinary skill in the art, with thebenefit of this disclosure, that various changes, substitutions andalterations can be made without departing from the spirit and scope ofthe disclosure. Any use of the words “or” and “and” in respect tofeatures of the disclosure indicates that examples can contain anycombination of the listed features, as is appropriate given the context.

While illustrative implementations of the application have beendescribed in detail herein, it is to be understood that the inventiveconcepts may be otherwise variously embodied and employed, and that theappended claims are intended to be construed to include such variations,except as limited by the prior art.

Reference throughout this specification to “one implementation” or “animplementation” means that a particular feature, structure, orcharacteristic described in connection with the implementation isincluded in at least one implementation of the present disclosure. Thus,the appearances of the phrases “in one implementation” or “in someimplementations” in various places throughout this specification are notnecessarily all referring to the same implementation. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more implementations.

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary implementations. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the disclosure asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

The invention claimed is:
 1. A matching network, comprising: afirst-stage matching network; a second-stage matching network having acontrol loop bandwidth representative of electrical components of thesecond-stage matching network; and a sensor element simultaneouslycoupled to both the first-stage matching network and the second-stagematching network, wherein: the first-stage matching network is toperform low-Q impedance transformations for time periods when changes inimpedance are outside the control loop bandwidth of the second-stagematching network, the second-stage matching network is to performimpedance matching for high-Q impedance transformations, and the sensorelement is to detect signals and make calculations that are used toalter electrical operating characteristics of the first-stage matchingnetwork and the second-stage matching network.
 2. The matching networkof claim 1, wherein the first-stage matching network includes a switchedmatching network and the second-stage matching network includes amechanically-tuned matching network.
 3. The matching network of claim 2,wherein the first-stage matching network uses at least one of fixedcapacitors and electronics wherein the switches may be at least one of aset of PIN diodes, silicon-carbide field effect transistors (SiCFETs),metal oxide field effect transistors (MOSFETs), insulated gate bipolartransistors (IGBTs), or bipolar junction transistors (BJTs) and thesecond-stage matching network may be at least one of a set of vacuumvariable capacitors or air variable capacitors and at least one of a setof stepper motors, brushed direct current (DC) motors, brushless DCmotors, or AC motors.
 4. The matching network of claim 1, wherein thefirst-stage matching network includes a continuously variable reactivetuning element.
 5. The matching network of claim 1, wherein the sensorelement measures voltage and current and calculates the relationshipbetween the measured voltage and current in both phase, magnitude, andimpedance.
 6. The matching network of claim 1, wherein the sensorelement operates a switch actuator to alter electrical operatingcharacteristics of the first-stage matching network.
 7. The matchingnetwork of claim 1, wherein the first-stage network includes animpedance transformer using a lumped-element, pi network.
 8. Thematching network of claim 7, further comprising: a plurality of switchterminals disposed on opposite sides of the pi network, wherein a firsthalf of the plurality of switch terminals are disposed on a first sideof the pi network and a second half of the plurality of switch terminalsare disposed on a second side of the pi network.
 9. The matching networkof claim 8, wherein a tunable range of the first-stage matching networkis modified responsive to altering a state of at least one of theplurality of switch terminals.
 10. The matching network of claim 8,wherein altering the state of at least one of the plurality of switchterminals includes opening or closing the at least one switch terminal.11. The matching network of claim 1, wherein the first-stage matchingnetwork and the second-stage matching network perform impedance matchingon the same or different parts of a modulated RF waveform.
 12. A plasmageneration system, comprising; a radio frequency generator; a matchingnetwork coupled to the radio frequency generator to generate animpedance-matched output, the matching network comprising: a first-stagematching network; a second-stage matching network having a control loopbandwidth representative of electrical components of the second-stagematching network; and a sensor element simultaneously coupled to boththe first-stage matching network and the second-stage matching network,wherein: the first-stage matching network is to perform low-Q impedancetransformations, for time periods when changes in impedance are outsidethe control loop bandwidth of the second-stage matching network, thesecond-stage matching network is to perform impedance matching forhigh-Q impedance transformations, the high-Q impedance transformationhas a Q factor that is greater than two and the low-Q impedancetransformation has a Q factor that is less than two, and the sensorelement is to detect signals and make calculations that are used toalter electrical operating characteristics of the first-stage matchingnetwork and the second-stage matching network; and a plasma chambercoupled to the matching network to receive the impedance-matched outputfrom the matching network.
 13. The plasma generation system of claim 12,wherein the radio frequency generator generates a modulated RF waveformand the first-stage matching network engages each state of the modulatedRF waveform while the second-stage matching network may engage on asingle state of modulated RF waveform.
 14. The plasma generation systemof claim 12, wherein the sensor element detects a change in plasmachamber impedance and responds to the change in impedance caused byhigh-speed variations to alter electrical operating characteristics ofthe first-stage matching network.
 15. The plasma generation system ofclaim 12, wherein the first-stage matching network includes a pluralityof RF switches.
 16. The plasma generation system of claim 12, whereinthe first-stage network includes an impedance transformer using alumped-element, pi network.
 17. The plasma generation system of claim16, further comprising: a plurality of switch terminals disposed onopposite sides of the pi network, wherein a first half of the pluralityof switch terminals are disposed on a first side of the pi network and asecond half of the plurality of switch terminals are disposed on asecond side of the pi network.
 18. The plasma generation system of claim17, wherein a tunable range of the first-stage matching network ismodified responsive to altering a state of at least one of the pluralityof switch terminals.
 19. The plasma generation system of claim 18,wherein altering the state of at least one of the plurality of switchterminals includes opening or closing the at least one switch terminal.20. The plasma generation system of claim 17, further comprising: amemory storing preset switch configurations for the plurality of switchterminals, wherein the calculations performed by the sensor elementinclude a lookup of at least one preset switch configuration based onthe detected signals.